1. Field of the Invention
This invention relates to hybrid electronic devices, and in particular to a high power thick film resistor which minimizes electric field density in desired locations.
2. Description of the Prior Art
Resistors and resistive elements fabricated with thick film technology are now well-known, and in widespread use in the electronics industry. Such resistors often take the form of a thick film of resistive material which is screen printed onto an insulating substrate. Spaced apart electrical connections to the resistive material cause the material to function as a resistive element between the electrical connections. After fabrication the part is tested and trimmed to the desired resistance. One known technique for trimming such resistors is to use a laser to vaporize a portion of the resistive material, and thereby force any current flowing through the resistor to flow through the remaining regions, creating a higher resistance.
Conventional thick film resistors have been fabricated with substantially parallel electrodes separated by the resistive element. Thus, when the resistor is trimmed, for example, by a laser machining operation, higher electric fields will be present near the edge being trimmed, often resulting in shorting or breakdown in high voltage operation. Furthermore, conventionally available thick film resistors are well known to suffer from hot spots, resulting from slight variations in the thickness of the thick film coating. In addition, the conventional thick film resistor has resistive material approximately one mil thick, and when trimmed, microcracking around the trim kerf is prevalent.